1. Field of the Invention
The present invention relates to a method and a terminal for communication over communication networks. More particularly, the invention relates to a method and a terminal for communication over a network having a low degree of privacy such as the Internet.
2. Description of the Related Art
The Internet is known as one of predominant networks connecting computers on a global scale. Specifically, the Internet is a computer network that interconnects wide area computer networks set up by corporations, universities and other institutions throughout the world. Diverse services such as electronic mail, file transfers and information searches are already available over the Internet.
FIG. 1 is an explanatory view outlining how the Internet is formed. In FIG. 1, portions enclosed by broken lines NET101, NET102, etc., represent computer networks. Each of the computer networks NET101, NET102, etc., has a plurality of terminals T. The terminals T on each computer network are connected to form a local area network (LAN). The LANs operate on a number of key principles such as the Ethernet and the token-ring.
The computer networks NET101, NET102, etc., are interconnected by means of routers R101, R102, etc. The routers R101, R102, etc., route data to their destinations between computer networks.
When the computer networks NET101, NET102, etc., are interconnected by the routers R101, R102, etc., in the manner described, they constitute a world-wide computer network called the Internet. The Internet allows the computer networks NET101, NET102, etc., around the world to exchange data therebetween.
The Internet typically utilizes the IP (Internet Protocol) as its network layer protocol. The IP involves assigning an IP address to each of the terminals configured on a network. All destinations to which data may be transferred are identified by IP addresses. An IP address comprises four groups of eight binary bits each, such as "43. 3. 25. 24. 6."
As the Internet expands ever wider, there is concern over an eventual shortage of IP addresses. On a network where a large number of terminals are registered but a relatively small number of them are actually connected at any one time, the IP address count may be economized as follows: The network is furnished with a server dedicated to assigning IP addresses to configured terminals. The server assigns IP addresses to terminals on the network only when they are actually connected. This arrangement eliminates the need for preparing as many IP addresses as all terminals on the network. A limited number of IP addresses may thus be utilized efficiently.
The Internet utilizes the TCP (Transmission Control Protocol) and the UDP (User Datagram Protocol) as its transport layer protocols. The TCP involves permitting communication after setting up what is known as a connection type communication link. The TCP offers such functions as packet sequencing, retransmission, flow control and congestion control. The UDP is a connectionless type protocol that is used in place of the TCP where there are real-time constraints. For example, digital audio communication is carried out in accordance with the UDP. In that case, the flow of audio data proceeds uninterrupted even if part of the packets involved drop out; retransmission of the missing packets is not requested under the UDP.
As mentioned, the Internet basically utilizes the TCP/IP protocols. Each of the terminals connected on a computer network is assigned an IP address for terminal identification. Packets are transferred between terminals according to the TCP or the UDP.
Individuals' personal computers are not always interconnected over a LAN. Without being connected to a LAN, these computers have no IP addresses. Where such individuals wish to join the Internet, they have recourse to an enterprise called an Internet service provider (called the ISP hereunder). Via the ISP, an individual's computer hooks up to a telephone line connected to a computer network which in turn is linked to the Internet in accordance with the PPP (Point-to-Point Protocol) and the SLIP (Serial Line IP).
FIG. 2 is an explanatory view sketching how an ISP is typically constituted. The ISP's computer network NET151 of this example comprises a server S151 and a router R151. The server S151 is connected to a public telephone network TEL151 via a plurality of modems M151, M152, etc.
Terminals T151, T152, etc., represent those of the individuals wishing to gain access to the Internet. The terminals T151, T152, etc., are connected to the public telephone network TEL151 via modems, not shown. These individuals' terminals are typically personal computers equipped with serial ports.
Where a user wishes to hook up to the Internet via an ISP, it is customary for the user to sign a contract with the ISP in advance. With the appropriate contract signed by both the user and the ISP, an account name and a password are provided to the user.
When any one of the individuals' terminals T151, T152, etc., is attempting to access the Internet, the user at the terminal dials a telephone number of the ISP to call the ISP's computer network NET151. When called up, the server S151 requests the input of an account name and a password to verify that the user in question is indeed under contract with the ISP.
When the entered account name and password are found to be correct attesting to the contract between the user and the ISP, the server S151 searches for an available IP address and assigns that address temporarily to the terminal (T151, T152, etc.). Using the IP address thus furnished, the terminal in question gains access to the Internet.
In the above example, PPP connections were shown to be established using telephone lines. Alternatively, the ISDN (Integrated Service Digital Network) may be utilized. The ISDN64 offers three channels per line: two B channels at 64 kbps and one D channel at 16 kbps. Where an ISDN arrangement is available, IP packets are allowed to flow over a B channel serving as a 64-kbps line. Because there are two B channels, a contract to use one telephone line of the ISDN effectively allows two lines to be used independently.
The Internet is available to anyone basically free of charge. An Internet telephone service using the Internet for making calls costs illustratively charges of the contract with an ISP, local telephone charges up to the ISP and usage fees of the ISDN. This means that long-distance and international calls are placed at significantly low costs if the Internet is utilized. Thanks to the moderate expenses involved, other communication services based on the Internet are also coming into use.
One problem with the Internet-based telephone communication is the inability to call up a user's terminal connected to the Internet on a PPP or like basis. Destinations of data transfers over the Internet are identified by IP addresses. However, users' terminals that gain access to the Internet under the PPP through contract with an ISP are assigned their temporary IP addresses only when they request connection to the network. These terminals have no permanent IP addresses assigned thereto. This means that if the first of two communicating parties usually connected under the PPP via the ISP has not currently established a PPP connection, the second parity attempting to connect to the first party under the PPP over the Internet has no way of knowing the IP address of the first party. It is thus impossible to call up the other party directly.
On the other hand, terminals of LANs run by corporations, universities and other institutions are connected to the Internet not via an ISP but directly. These terminals may call up one another using appropriate IP addresses whenever needed because their IP addresses are permanently assigned and they operate at all times.
Some of these LAN terminals work under the DHCP (Dynamic Host Configuration Protocol). That is, a server on the LAN assigns available IP addresses to only those terminals that are actually connected to the network, whereby the number of IP addresses is economized. Such terminals, even if they are part of a LAN of a corporation or a university, are thus assigned only temporary addresses instead of permanent, unique IP addresses. When someone wants to call any one of these terminals, it is impossible to place the call because the target terminal's IP address, unlike an ordinary telephone number, cannot be known beforehand.
One solution to the problem above is provided by use of the so-called rendezvous server or like service capable of affording the calling party a necessary IP address of the destination party. A party wishing to utilize such a service first turns on his computer and logs onto the server. The calling party then requests a list of currently logged-in parties under the service contract to be sent from the server. Looking at the list, the calling party selects an appropriate party to communicate with and informs the server thereof. In turn, the server furnishes the IP address of the selected party. Using the IP address thus acquired, the calling party then goes into end-to-end (PPP) communication with the desired party.
Making use of such services for communication over the Internet involves the following major disadvantages:
(1) Two parties wishing to communicate with each other must turn on their computers and register with the appropriate server of the service such as the rendezvous server before communication can take place. Once a party is put on the list, removing power from the party's computer does not automatically erase the terminal from the list. In other words, finding a party in the list does not necessarily mean that the party in question has logged in and is ready to communicate.
(2) Server usage charges need to be paid.
(3) Each party's log-in information (i.e., IP address) registered with the server is effectively left open to the public. There is little possibility of keeping one's privacy.
(4) Because the contracted parties' IP addresses are all disclosed in the list, unnecessary calls may arrive unsolicited from terminals other than those one may wish to communicate with.
(5) If the server shuts down, no communication can take place.
The Internet is what is known as an open network that only offers a limited degree of privacy in the communication of data. To secure highly private communication over the Internet generally requires that the terminals concerned exchange beforehand encryption information or data compression information to ensure privacy. Communication is subsequently carried out on the basis of the encryption information or the like thus exchanged.
The above measure for communication privacy is not quite secure because the encryption information transmitted over the Internet can be intercepted by an unscrupulous third party. If the encryption information is decoded, there is no privacy of communication.
To secure privacy of communication, it is generally necessary to use encryption methods or data compression schemes involving sophisticated algorithms that are difficult to decipher. In any case, it is no easy task to acquire a high degree of privacy in communication over the Internet.